Fastening objects together through methods incorporating threaded nut and bolt structures is well known. Typically, a male-threaded bolt projection from a first item is passed through an aperture in a second item, and a threaded nut is rotated onto the bolt projection until the bolt tightly compels the second item against the first item to form an assembled structure. Problems arise in maintaining the integrity of the resultant structure, as well as the individual components. For example, operational vibrations from use of the resultant structure may become translated into rotational movement of the nut relative to the bolt that loosens the bolt. Using a deformable insert component to provide a locking effect upon the threads of the nut and bolt assembly is well known in the art. One example is U.S. Pat. No. 3,938,571 to Heighberger for a “Nut with Sealing Insert.” Alternatively, rigid metallic locking devices have been used, which apply frictional locking forces upon the bolt member threads. An example of this type of device is U.S. Pat. No. 4,069,854 to Heighberger for “Locknut with Segmental Locking Elements.”
However, the prior art methods and structures have structural and functional disadvantages. Significantly, in the prior art, nut thread area is lost in order to allow for insertion of the locking element. For example, a conventional two-inch thread-nut has two inches of total body length and thread length along its central axis C. The prior art two-inch bolt with locking component also has two inches of total body length, but formation of a mounting void for containing the locking component results in a corresponding reduction of thread length. This shortening of thread length results in a reduction in structural strength in the nut which, in turn, results in a higher rate of nut thread failure when compared to a nut with a conventional (and therefore longer) thread length. Although the reduction in strength is dependent upon other factors, such as type of assembly and nut materials, it has been found that, as a general rule, a 25% reduction in thread engagement length can result in a 25% reduction in performance strength of a nut.
Another disadvantage with structures and methods utilizing a rigid locking insert is that the rigid member distorts the bolt threads through compressive force. This distortion results in damage to the bolt, which cannot be reused, and, therefore, the assembly cannot be disassembled and reassembled. This type of assembly is only useful for a single use or permanent installation, and is not available for uses that may require disassembly and re-assembly.
A further disadvantage of the prior art locking members is that a structural retaining element must physically and firmly retain the member within a member-carrying void during shipping and transport of the lock nut; otherwise, the member may become separated and lost. Similarly, a retaining structure is also needed to hold the member in place within the member-carrying area of the lock nut while the nut is being rotated about a threaded bolt member, and importantly during removal of the nut from the bolt. Prior art nuts, such as the aforementioned Heighberger “Nut with Sealing Insert”, utilized a machine-knurled edge to “grip” the member during transport, application and removal. However knurl patterns formed by machining techniques have limited knurl element height, width and depth dimensions and, consequently, limited member retaining capabilities. The member often becomes separated and may be lost during shipping. More importantly, the “gripping” abilities of the machine-knurled patterns are limited and insufficient to impart the frictional forces required to rotate and remove the deformed member from a bolt as the nut is rotated off of a bolt. Consequently, a user must find another mechanical means to engage and remove the deformed member from the bolt, resulting in greatly increased time for removal and disassembly.
Other prior art nuts utilize a cap member element, which is formed over a portion of the top surface of the locking member and holds the member within a carrying void, to retain the member during transport, removal and disassembly. An example of such a prior art nut is the ESNA® NU locknut. The ESNA cap member also exerts frictional forces upon the surface of the member to help compel it to rotate about a threaded bolt as the nut is rotated about the bolt. It is readily apparent that such a structure requires an additional sacrifice of effective thread length by consuming corresponding nut body material for the formation of the cap member. Also, the presence of this fixed and rigid cap structure makes replacement of an individual locking member impossible and, where the member has been degraded or failed, the entire nut must be discarded and replaced.
Additionally, it is the compressive interaction of the projections, member-carrying void and the bolt threads that causes the deformable ESNA member to impart locking characteristics to the ESNA lock nut. As a result, the deformable member cannot freely rotate about the bolt threads, but instead must deform as it travels about the bolt. This deformation results in a great deal of frictional force that must be overcome as the ESNA nut is threaded onto or off of the bolt. Similarly, the member must deform and becomes structurally altered immediately upon application of the nut onto a bolt.
Furthermore, the frictional force exerted upon the bolt threads by the ESNA-type locking member is limited to a constant value resulting from the compressive forces exerted upon the member through the cap/void wall/bolt thread interaction. This frictional force value reaches a maximum value once the bolt threads engage the entire thread-engaging inner surface of the deformable member. It is apparent that this value will not be increased by further tightening of the nut upon either the bolt or upon a workpiece disposed about the bolt, since this tightening will not increase the compressive forces imparted to the member by the cap/void wall/bolt thread interaction. Moreover, as the deformable member travels along the bolt threads, frictional abrasion from the bolt threads degrades the deformable member. Therefore, the maximum frictional force value imparted by the deformable member upon the bolt threads decreases every time the nut is tightened or loosened about a bolt member. Eventually, the member will be degraded beyond a point of meaningful frictional engagement with the bolt threads and, since the ESNA nut structure does not provide for replacement of the deformable member, the entire nut and member assembly must be discarded and replaced. Therefore, the prior art ESNA-type nut is not preferred for applications requiring a large travel distance along the bolt threads for application, nor for those applications requiring disassembly and re-assembly of the nut/bolt structure.
Another desired characteristic is a vibration dampening function. The other prior art nuts limit their vibration-dampening characteristics to absorbing vibrations between the thread bodies of the nut and bolt. This type of dampening may be insufficient in some applications, and additional vibration dampening devices may be required between nuts and workpieces in order to ensure that the prior art lock nuts remain in a fixed position when the assembly is subject to operational vibrations.
What is needed is a locking nut that has the thread engagement strength of a comparable standard non-locking nut. What is also needed is a locking member that does not distort and thereby damage the threads of the nut or bolt member. The nut must also retain the locking member during shipping and transport, and during rotation about a bolt and, more importantly, during removal of the nut from an assembly. What is also desired is a locking member that freely travels over bolt member threads until the member reaches a locking engagement point, thereby avoiding degradation of the member during assembly and disassembly. It is also desired that the lock nut provide vibration-dampening qualities beyond the thread engagement areas and including the nut-to-workpiece interface, in order to provide adequate locking and vibration dampening and resisting characteristics. And lastly, it is desired that the a user may vary the amount of locking force required to lock the locking nut in position, and thereby also vary the force imparted to the final assembly by the locking member.